BMWBLOG Analysis: 2012 BMW M5 Transmission Choices

Well what’s all this brouhaha over the next M5’s transmission choices. A little logic may help in understanding what the possibilities will be. Let’s start with what …

Well what’s all this brouhaha over the next M5’s transmission choices. A little logic may help in understanding what the possibilities will be. Let’s start with what we know and what we’re willing to bet the farm on.

1. The engine in the next M5 is the S63B44 capable of producing 530 lb-ft of torque (approximately 717 Nm).

2. BMW will work with their current vendor pool to source the transmission.

3. BMW is conservative and the torque handling capabilities of the transmission will exceed the flywheel torque of the engine by a healthy margin.

We’re more than sure that the S63B44 will be the engine in the next M5. It’s received great critical acclaim in the X5M and X6M models. It also produces a ton of torque from fairly low RPMs through fairly high RPMs. More like a torque plateau than a torque peak.

BMW currently works with ZF and Getrag to supply gearboxes. Both can supply manuals, automatics and dual-clutch transmissions. But the subset of their transmissions that can provide the torque handling BMW would prefer is fairly small.

So, currently the X5 and X6 Ms use the ZF 6HP32 which can handle 1000 Nm of torque. That’ll give us what BMW considers to be the minimum torque handling capacity they’re willing to live with. And yes, the 6HP32 would plug right into the new M5.

ZF’s six speed in the 135i, 335is, and the M3 can handle peek torque of around 600 Nm. So the manual is out. Does anybody make a manual that can handle the ‘awesome’ torque of a BMW turbo engine? Well sure, that and more actually – Tremec makes a really great 6 speed manual and has introduced an enhanced torque handling capacity box called the Tremec T56 Magnum. It’s one stout gearbox. Tremecs are used in ‘vettes and while they can feel balky at slow speeds and light loads they come alive under power. Good gearboxes, but as far as we know BMW doesn’t use Tremec as a supplier. You could also go a little nuts and get a 5 speed Jerico gearbox, but that’s too NASCAR for any German car company.

But there are alternatives. Getrag makes a 7DCL750 dual-clutch that handles 750 Nm. Scratch that one off the list. ZF makes the 7 DCT 50 which can handle a peek of 1000 Nm. Oh, keep that one one the list. ZF also makes the 8HP which we believe can handle a peek of 1000 Nm.

But that’s an automatic right? Well it can be. But the torque converter can be swapped for a automated clutch. OK – so an 8 speed DCT! Not so fast, we don’t know if the automated clutch assembly for the 8HP changes the torque handling capacity. But, in a bet the farm move (I know longer own the farm), I suspect it’ll be an 8HP that ends up in the M5.

Why?

Because of what the two additional overdrive ratios do for EfficientDynamics.

10 responses to “BMWBLOG Analysis: 2012 BMW M5 Transmission Choices”

Just a quick comment – ZF shows, on its website, that the 8HP is capable of handling 750 Nm of torque. We believe, without any certainty or inside knowledge, that it can be made capable of handling more peak torque.

Steven,
We have requests for info into BMW for an article on software/electronics. While we don’t know the specifics for each model, I can say that the cars using the N54 engine use a VDO ecu (Continental owns VDO now, IIRC). The ecu is only one of many ‘computers’ in the car, and they all are on CAN buses with the CAN buses integrated via a FlexRay bus (FlexRay isn’t in all models yet). Coding probably is done partially by suppliers and completed/tweaked by BMW. Believe it or not, electronics/software represents a HUGE portion of the costs for building a car these days.

as long as the M products have dual clutch transmissions i’m sold on them, otherwise meh, the audi a4 with 8 speed auto transmission feels ok, but could have been better with a dual clutch transmission.